Fire commissioner Lloyd Ayers said this afternoon that emergency workers will continue searching for victims buried in the debris by using two police dogs to trace human smells and additional workers to sift through the pile of rubble.

"We're getting fresh personnel and staffing here to dig and we've had two dogs to come out and work the pile to locate others so we know exactly where to dig," Ayers said at a press conference.

Ayers said he expects workers to continue digging at the site for 12 to 24 hours, until they are sure that no individuals remain buried.

"Let's again keep in mind that we did not know and do not know how many people were actually in the thrift store," Mayor Michael Nutter said this afternoon. "That is why the fire department search and rescue operation continues."

The building was in the process of being demolished when an exterior wall that it shared with an adjoining building fell outward today, collapsing into the ajoining two-story building that housed a Salvation Army Thrift Store. The thrift store was damaged but is still standing.

Officials at the University of Pennsylvania hospital, which treated five victims, said that they saw mostly cuts and bruises on victims taken there. At least one victim has already been released, and others are expected to be discharged today.

Datner said that most of the victims were in the thrift store at the time of the collapse.

"They were a bit stunned, they were saying they heard a loud noise and then the ceiling began falling," Dr. Elizebeth Datner said at a news conference. "We saw one individual who had been trapped, but they are all talking and all in stable conditions."

At least one injured individual was a crane operator working on the demolition of the building, WPVI reported.

Eyewitness Mark Newell told the Philadelphia Inquirer that the building collapse sounded like an "unbelievable rumble" that was "like a freight train," according to the newspaper.

He said he could hear people moaning from inside.

Brian Mullins told the newspaper that he was unloading paint from a van at a nearby building when he heard the collapse, and he rushed to help pull six people from the rubble.

"I just wanted to get people out," he said. "The dust was so thick you couldn't see in front of your face," he said.

The vacant mixed-use commercial building was in the process of being demolished when it collapsed, according to city inspector Carlton Williams. Authorities are unsure how many construction workers were at the site when the building collapsed.

"We want to be sure to keep the focus on the firefighters that are actively engaged in search and rescue," Nutter said earlier today. "We had a significant number of people on the scene, and we will continue this operation until we are certain that anyone who was in the building has been taken out of building and is recovered."

Firefighters were first dispatched to the building at 10:43 a.m. and arrived at 10:45 a.m. to begin working, Ayers said.

A 10-block stretch of Market Street, which runs through the city, was shut down for the rescue effort.

Williams said that both the building's owners and the contractors had all of their permits and paperwork in order and up to date, and the building had no prior code violations.